1. Field of the Invention
The present invention relates to a developing agent recycling technique in a charging device capable of switching and executing charging processing for a photosensitive surface of a photosensitive member and collection processing for a developing agent remaining on the photosensitive surface.
2. Description of the Related Art
An image forming apparatus such as a so-called electrophotographic apparatus or an electrostatic printer performs, after forming an electrostatic latent image on a photosensitive member, image formation processing by electrostatically depositing a developing agent on the electrostatic latent image and transferring a developing agent image onto a sheet. Since the electrostatic latent image and the developing agent not fully transferred remain on the photosensitive member after the transfer, the image forming apparatus removes this remaining developing agent with a cleaning device and subsequently removes the electrostatic latent image with a charge eliminating device. According to U.S. Pat. No. 5,051,332, there is disclosed a technique for reducing a size of an apparatus using a cleanerless developing device that simultaneously performs, when an electrostatic latent image on a photosensitive member passes the cleanerless developing device, development of the electrostatic latent image and cleaning of a developing agent remaining after the last transfer.
According to JP-A-4-86883, there is disclosed a technique for providing, in a cleanerless system for not bringing a cleaning blade into contact with a photosensitive member, a member such as a brush for nonpatternizing a transfer residual toner and applying an AC bias in a mode for discharging a toner accumulated at least on the member to realize prevention of soil in an image forming apparatus.
In a magnetic brush charging system, as in the technique described above, a transfer residual toner is caused to adhere to a magnetic brush related to charging processing while the transfer residual toner is nonpatternized. Thus, it is necessary to execute a mode for discharging a toner at the time of nonprinting. In particular, in printing with a high printing ratio and continuous printing, uniformity of charging may be spoiled by adhesion of the transfer residual toner before the mode for discharging a toner is executed.
In the conventional cleanerless system, the nonpatternized transfer residual toner is returned to a developing device in a state in which the transfer residual toner is caused to adhere to the photosensitive member. Thus, although the cleanerless system has the same effects (no waste toner and environment-friendly) as recycling in the cleaning system having a blade, the execution of the mode for discharging a toner adhering to the magnetic brush affects productivity (print volume).